Air core meters are advantageously used as instrumentation gauges to provide readings of parameters of interest that are derived from sensors. For example, instrumentation gauges of this type are commonly found in the instrument clusters of automotive vehicles.
While such gauges are quite reliable and accurate in use, the process of making them requires particular care in assembling the pointer to the rotor. The pointer must be carefully pressed onto the rotor contemporaneously with an energization of the meter that produces a desired angular positioning of the rotor. If any twist occurs while the pointer is being pressed onto the rotor, the pointer must be pulled off and the step of assembling the pointer to the rotor must be re-attempted.
It is typical practice in the industry for the gauge manufacturer to perform the step of assembling the pointers to the air core meters in this manner. Thus, an automotive vehicle manufacturer typically orders from the gauge manufacturer gauges that include the pointers. However, this course of dealing imposes certain restrictions on the automotive vehicle manufacturer. One restriction resides in the styling of instrument clusters of automotive vehicles; another in spare parts inventory.
An example of the effect of such restrictions is illustrated by the case of a speedometer. Presently an air core gauge used for a specific speedometer application must be styled as a unique stand-alone assembly that has a specific graphic overlay. For service, it is necessary that the same unique stand-alone assembly be inventoried as a replacement speedometer. Considering the fact that there are many unique speedometer applications each requiring a unique stand-alone assembly, one can appreciate that spare parts inventories must include many different models and part numbers for spare speedometers. That the magnitude of this situation is quite large is perceived when one recognizes that many automotive vehicles contain more air core gauges than just merely speedometers.
For example, many vehicles also contain air core meter type tachometers as unique stand-alone assemblies. Yet the only difference between an air-core type speedometer and an air core type tachometer may be the different indicia on their respective graphic overlays. In the case of sensor-driven air core gauges, the only difference between two gauges, other than possibly a difference in graphic overlays or pointer styling, may be the values of their respective calibrating resistors for matching each to a respective sensor. Another potential area of difference may arise due to the fact that some air core meters are sensor-driven while others are sine-cosine type.
The present invention will greatly simplify the complications that now exist due to the many unique assemblies that must be inventoried. Briefly, the invention relates to a new and unique mounting of the pointer on the rotor of an air core type instrumentation gauge. A driving hub is fitted to the rotor of the air core meter movement such that the hub is at a proper circumferential position on the rotor. The pointer has a driven hub which can snap on and off the driving hub and which is circumferentially keyed to the driving hub so that the pointer is properly circumferentially positioned to the rotor. This mounting allows the pointer to be assembled to the air core meter after a graphic overlay has been disposed over the meter. Thus it becomes possible for the automotive vehicle manufacturer to order from the gauge manufacturer, air core meters which have only the driving hub, and not the pointer, mounted on the rotor. Automotive vehicle manufacturers and service organizations can use these "pointerless" meters in any applications that are appropriate, and they themselves assemble the pointers to the driving hubs. Inventory and part numbering requirments are simplified, because rather than having to stock a unique gauge for each specific application, it is possible for a particular "pointerless" meter to be used in any one of a number of different gauges which may differ only in graphic overlay or pointer styling. If a meter in an existing gauge needs to be replaced, the pointer is simply unsnapped from the driving hub of the meter that is being replaced, that meter is replaced by another, and the pointer is snapped onto the driving hub of the latter meter with full assurance that the pointer is properly circumferentially oriented to the meter's rotor. It is contemplated that only two types of meters need be stocked for service, namely sensor-driven and sine/cosine. When the movement of an existing gauge is being replaced, the graphic overlay and pointer of the gauge can be re-used.
The invention is especially conducive to the integration of multiple gauges into an instrumentation display which has a single graphic overlay. Such a display can be fabricated without an individual border surrounding each gauge thereby allowing the graphic legends to be made larger for better readability and styling appearance. Whenever an individual gauge requires replacement of a movement, its pointer is simply unsnapped from the hub of the movement being replaced and thereafter snapped on the hub of the new movement.